Researchers Grow Human Blood Vessels from Blood Cells

Action Points

Explain to interested patients that many forms of tissue damage are associated with a loss of vasculature.

Note that this study suggested that a combination of progenitor cells may be able to form new blood vessels, potentially offering a way to restore blood flow to damaged tissue.

Caution that the study took place in animals and more research is needed.

BOSTON, July 18 -- Researchers here have successfully grown functional and long-lasting blood vessels using progenitor cells from the blood or bone marrow of adult humans.

Although the research vessels were grown in mice, the finding is a key step toward engineering of vascular tissue for clinical uses, Joyce Bischoff, Ph.D., of Children's Hospital Boston, and colleagues, reported in the July 18 issue of Circulation Research.

"Our goal is to move into the setting of tissue regeneration" with the new technique, Dr. Bischoff said, although she noted that more research is needed before the process can be used in the clinic.

But she said using cells from blood or bone marrow means it's possible to avoid sacrificing other forms of tissue, such as veins or arteries. "It's much simpler just to draw blood and get all the cells you need to build new blood vessels."

The technique involves injecting a mix of endothelial and mesenchymal progenitor cells, suspended in a medium that forms a gel at body temperature.

When the cells were injected into immune-deficient mice, they formed blood vessels within a week, Dr. Bischoff said. "The neat thing is that they knew what to do on their own," she said, without the addition of growth factors or other substances.

The new blood vessels were completely human and swiftly formed links with the host vasculature, allowing red and white blood cells to pass through, Dr. Bischoff said.

Earlier studies had shown that endothelial progenitor cells from the blood could form blood vessels, but only if they were implanted at the same time as smooth muscle cells.

In those studies, the endothelial cells formed the inside of the vessels, while the muscle cells formed a perivascular outer covering, the researchers said.

To avoid using muscle tissue, Dr. Bischoff and colleagues turned to mesenchymal progenitor cells, which can be isolated from a blood sample or from bone marrow.

Immune-deficient mice were implanted with differing proportions of endothelial and mesenchymal progenitor cells, they said.

At a ratio of 40% endothelial and 60% mesenchymal cells, the implants developed an average blood vessel density of up to 119 per square millimeter, which was the highest observed, the researchers said.

When just mesenchymal cells were included in the mix, blood vessels also formed, probably as a result of secretion of vascular endothelial growth factor, but they were mouse blood vessels recruited from outside the gel.

The density of human blood vessels formed with the 40:60 mix was significantly greater (P<0.05) than the density of murine vessels formed when just mesenchymal cells were used.

As expected, no blood vessels were seen when just endothelial cells were injected, the researchers said.

To see how long the network of blood vessels lasted, they harvested the implants after seven, 14, 21, and 28 days and quantified the density of the blood vessel network.

Between days seven and 14, there was a nonsignificant decline in the density of blood vessels, they found, but after that the density remained stable at about 87 vessels per square millimeter.

In the long run, Dr. Bischoff said, such an approach might be used to speed wound healing, improve skin grafting, help repair damaged muscle -- "any place where there's ischemia."

One obstacle to clinical use of the technique is the length of time it takes to form blood vessels, she said, adding that speeding up the process is the subject of current research in her lab.

The study was supported by the U.S. Army. Dr. Bischoff and colleagues reported no conflicts.

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